Art of duplex wireless telegraphy.



No. 772,879. ,PATENTED' OCT. 18, 1904 I L. DB FOREST.

ART OF DUPLEX WIRELESS TELEGRAPHY.

APBLIQA'TIIQK 311.21) ssrcr. 21,1303.

N0 MODEL.

Mk ATTORNEY WITNESSES." Y 'INVENTOR g Leg deForestQ I v 5r I Patented October 18, 1904.

PATENT- OFFICE.

LEE DE FOREST, on NEW YORK, n. Y.

ART OF DUPLEX WIRELESS TELEGRAPHY.

. SPECIFICATION forming part of Letters Patent No. 772,879, dated October 18, 1904.

Original application filed June 4, 1903, Serial No. 160,026.

My invention relates to a method of operating spark telegraphy apparatus whereby a signal may be sent-and another received at the same time without oneinterfering with the other and also whereby the delicate receiving'apparatus may be protected against the powerful radiations of the associated sending apparatus.

The scope of my invention will be indicated in the accompanying specification and particularly defined by the claims terminating the same.

The drawings accompanying herewith illustrate preferred means for carrying out my invention.

Figures 1, 2, and 4t show devices for carrying out my invention, using an alternating generator as the source of electromotive force; and Fig. 3 shows means employing a source of continuous e'lectromotive force and an interrupter.

The figures do not,. however, show all the forms of devices-adaptable for carrying out 'iny invention, but'do show simple andv practicable means which clearly illustrate what the invention consists of.

In the drawings, A represents the transmitting-antenna, vA the receiving-antenna, and E the'earth connections for the same.

The receiving apparatus also includes waveresponsive and indicating devices of any suitable construction. The wave-responsive device should be of a type which is not injured by the strong impulses from the adjacent transmitter and is preferably a device of negligible resistanceand one which is self-restoring or always operative, requiring no decohering or adjusting to restore it to operative condition. I have herein shown the same as a Rutherford magnetic detector or responder 'R of negligible resistance, which fulfils these requirements, and the indicating device as a telephone-receiver H. This magnetic detec- Divided and this application filed September 21,1903. $erial No. 173,971.

N0 model.)

tor, as shown in Figs. 1, 2, and 4, consists of a core of fine magnetizable needles or wires 1, a coil. 2, which is in the antenna-circuit, and means for producing a variable magnetic field such, for .instance, as the magnet N, which is revolved by any suitable means, such as a motor M, either electric or mechanical.

The solenoid R is surrounded by a coil 3,'

the antenna A impulses designed forthe production and radiation of proper signal-transmitting waves.

Each 'dot or dash of a signal as produced by the transmitter consists of a series of sparks,

often or generally having a regular frequency of recurrence which may be controlled or predetermined. Each individual spark produces a wave train or series of electric oscillations, andeach signal element (dot or dash) consists of a large number of such wavetrains separated by an interval of time which is large as compared'with the time of duration of the spark.

If the signal-indicating member or members of the receiving apparatus be cut out of the circuit from the antenna to the earth,'or if a shunt be established about these members for a time coinciding with the duration of each individual sparkthat is, during the time of radiation of the transmitting-waveand if the normal condition be restored between each individual spark, then the influence which the heavy radiation from the closely adjacent transmitting-antenna would otherwise have upon the receiving apparatus will be prevented.

As the duration of the spark is very short-- say one one-millionth of a secondthe interruption in the receiving-circuit need be of but a very brief duration, and the chance of the receiving apparatus losing a signal is very small, as for this to occur the spark frequency must be equal to that of the received impulses and be in phase therewith. To further guard against this, it is preferred that'one set of apparatus, consisting of a transmitting apparatus at one station and a receiving apparatus at the other station, have a spark frequency differing from the other set of apparatus. As an illustration one transmitter may have a spark frequency of forty per second, while the transmitter at the other station may have a frequency of sixty-five per second. In this case it is impossible for the two to get permanently into step or phase, and if the impulses produced by one or two sparksat a transmitting-station are thus rendered ineffective at the other receiving-station this will be insufficient to cover all of any signal element, and the remaining impulses will be sufficient to render the signal audible.

. In Fig. l the transmitting apparatus comprises an alternatingcurrent generator 1), switch C, step-up transformer T 'l", sparkgap S, and condensers K. inserted between antenna A and earth E. Any other suitable type of transmitting apparatus may, however, be employed. To the shaft of the alternating-current generator is secured a commutator or switch F, which, as shown, consists of a wheel or disk placed in circuit with the wave-responsive device and having insulated segments in its periphery. A brush f, also in the same circuit, engages the periphery of this disk as it revolves. Conductors O and 0 respectively connect the brush with the antenna and the shaft or body of the disk with the solenoid-coil of the magnetic detector or to whatever type of wave-responsive device is employed. When the brush f bears upon an insulating-section, the receiver is momentarily disconnected from the antenna. hen the brush rests upon the metal parts between the insulating-sections, the receiver is momentarily connected to the antenna.

Fig. 2 shows the same construction except that here the antenna is always connected to earth through the primary of a transformer the secondary of which includes the detector or receiver R and the brush and commutator Fig. 3 shows a construction employing an induction-coil D and battery B, in which the wave-responsive device or receiver is shunted at the instant of sparking of the transmitter by a shunt of Zero resistance and zero impeber I of the interrupter carries a section or plate P, which is insulated from the body thereof, as by an insulat'ing-section I and forms one terminal of a shunti ng-circuit Y. A contactpoint J, constituting the other terminal of the shunting-oircuit, is so placed as to be engaged by the plate or section 1 in its vibration to momentarily close the circuit.

Fig. at shows a construction like that in Fig. 1, except that themagneticdetector isol somewhat dilferent construction. In this case the core consists of a band L, of magnetizable n1aterial, which passes over wheels 5 5, turned from a motor M in any suitable manner. The magnet N in this case need not turn. This closing of the circuit or cutting outol' the indicating instrument should be so timed as to occur with or but little preceding the beginning of the spark at S and to terminate with or but little after the spark. Numerous other ways of securing this momentary cutting out or shunting of the indicating instrument at the instant of sparking of the nearby transmitter may be employed. For example, it an alternating generator situated at a d istanee from the receiving mechanism be employed a, synchronous motorenergized from this alter nating current, and therefore always in phase with the transmitter-current, may be employed to drive the switching or shunting commutator. it is not necessary to l'urther illustrate the same here.

\Vhat 1 claim as my invention is 1. The method of silmiltaneously sending and receiving messages a ta wireless signalingstation which consists in breaking the receiving-circuit at the beginning of each spark of the transmitter and restoring it at the termination of each spark.

2. The method of simultaneously transmitting and receiving a message at the same station which consits in employing dill'erent spark freq uencics for the transmitting and the receiving waves, and in cutting the receiving device out of its circuit during the time of each spark and restoring it in its circuit be tween each spark.

3. The method of simultaneously transmitting and receiving a message at the same station which consists in employing dill'erent spark frequencies for the transmitting and the receiving waves, and in isolating the indicat ing device of the receiving apparatus from the effects of waves produced by the associated transmitter during the time of duration of each spark and in sulm'iitting the indicating device to such influences between (:lt'll spark.

in testimony whereoll have hereunto allixed my signature, this 9th day of Septeml )er, ltltlii, in the presence of two witnesses.

LEE [)lC FORICS'I.

Vitnesses:

Gnonen \V. 'luonAs, H. L. Rnrxonns. 

